Throughout the world there are deposits of petroleum residues that are created artificially or naturally. For example, Bahrain pitch derives from the black oil residues of the Caltex Petroleum Corporation refinery [now operated by the affiliated Bahrain Petroleum Company B.S.C. (closed)] located in Sitrah, Bahrain (the largest island of the Bahrain group of islands), generated in the 1938-1942 time period. The residue, apparently with brackish quench water, was deposited in this time period in seven (7) pits creating seven (7) pitch ponds having a total area of about 70,000 square meters. The only changes to this resting body of pitch over the years since 1942 are those gently wrought by natural forces, such as the dusting over by desert sands, evaporation from the searing Asia Minor (Middle East) heat and deposition of rain water and migrated sea water. The black oil residues deposited in the pits were compositionally relatively consistent because they were made primarily over a short period of time while the refinery was being limited to the manufacture of aviation fuel and other "light" cracked hydrocarbon feedstocks. Variability in the pitch was inputted when, during that period, untreated crude oil was fed through the refinery and then deposited into the pits. Thus, "Bahrain pitch", as that term is employed herein and in the claims, means the pitch collected and located in the aforementioned seven (7) ponds, as it was generated in the W.W.II timeframe and modified by natural forces in subsequent years to the year 1987. Its unique past establishes the pitch to be an unique material.
Essentially all of the other black oil residues deposits about the world are "newly" created relative to the creation of the Bahrain pitch ponds. Hardly any of them are more than 30 years old and most of them were formed from residues of a highly diverse nature reflecting the advances in petroleum technology in the years between the formation of Bahrain pitch and this more recent period. Consequently, they possess compositions materially different from Bahrain pitch. The differences in chemical composition of Bahrain pitch from other black oil residue deposits can be seen from the differences in physical properties of Bahrain pitch and the other black oil residue deposits. One factor that stands out about Bahrain pitch is its high viscosity. In this regard, Bahrain pitch's viscosity fits somewhere between conventional residue deposits and the naturally occurring bitumens used primarily for making asphalt. This high viscosity is a reflection of the pitch's unusually high paraffinic and crystalline wax contents and its high asphaltenes content. Most of the world's black oil residues contain individually no more than about 10 weight % of these materials whereas Bahrain pitch contains more than about 20 weight % of them. In addition to this high wax and asphaltenes content, Bahrain pitch has an inordinately high crystallized carbon content.
The special black oil residues used in forming the Bahrain pitch coupled with the environmental considerations extant during the history of the ponds caused to be generated a unique composition of matter. The quiescent state of its existence allowed the Bahrain pitch to undergo a transformation not unlike that which occurred in naturally-occurring asphaltic bitumens that one finds in countries such as Venezuela and Trinidad. Of course, the limited age of the Bahrain pitch ponds precludes the pitch from reaching the ripe physical state of these other natural bodies. Even so, aromatic molecules within the pitch benefited from the extended quiescent condition to become aligned into large anisotropic bodies which contribute to the pitch's high viscosity. Though such transformation is interesting chemistry, it however transformed Bahrain pitch from a material which theoretically could have been readily exploited for its fuel value. To date, very little of the Bahrain pitch ponds has been mined for any purpose whatsoever and none of that has been for an effective commercial gain.
Unrefined Bahrain pitch has a high viscosity in the range of greater than 40,000 centistokes, as determined at 150.degree. F. (65.6.degree. C.), greater than 6,000 centistokes, as determined at 125.degree. F. (79.degree. C.) and 2-5,000 centistokes, as determined at 200.degree. F. (93.degree. C.) Its A.P.I. at 60.degree. F. (15.5.degree. C.) is less than 0, calculated to be typically -6 to -10 A.P.I.
Unrefined Bahrain pitch comprises as major constituents,
2 to 10 weight percent of total sediments including siliceous particulate matter and carbon particulate matter (generally viewed as crystallized colloidal carbon), PA1 8 to 12 weight percent of paraffinic and microcrystalline waxes, and PA1 20 to 25 weight percent of asphaltenes.
The following table sets forth a summary of the composition and known properties of the Bahrain pitch:
TABLE 1 ______________________________________ Typical Specifications from Bahrain Pitch Ponds Neat Pitch 5%.sup.* 10%.sup.** 15%.sup.*** ______________________________________ Viscosities @ 38.degree. C. Centistokes &gt;20,000 11,000 1,500 900 Redwood (sec.s) 95,000 52,250 7,125 4,275 Saybolt (sec.s) 85,000 46,750 6,375 3,825 Ash Content, w/w max. 0.1 0.1 0.1 0.1 BS & W, % w/w max. 1 1 1 1 Sulphur Content, % w/w 4.9 4.7 4.4 4.2 Flash Point .degree.C. 129 61 61 61 Pour Point .degree.C. 42. 29.3 27.1 15.0 .degree.F. 107.6 86. 81. 59. Asphaltenes, % w/w 24 23 22 20 ______________________________________ .sup.* Diluted by that weight % by diesel or light cycle gas oil. .sup.** Diluted by that weight % by diesel or light cycle gas oil. .sup.*** Diluted by that weight % by diesel or light cycle gas oil.
It has been known for some time that the practical limit for cutting unrefined Bahrain pitch with light cycle gas oil or diesel oil is 15-18% w/w. Above this figure precipitation of asphaltenes from solution was recognized as occurring.
The Bahrain pitch as found in the ponds has a significant particulates sediment content ranging in the area of 2 to 10 weight %, give or take a percent, based on the weight of the pitch. Of this sediment content, the inorganic oxide content of the sediment ranges in the area of 0.25 to 5% by weight of the pitch. The inorganic oxide content should be reduced in refining the pitch to the first stage, to between 0.05 to 0.1% by weight of the pitch, and preferably a lesser amount. The remainder of the sediment content of the pitch is particulate carbon matter, such as crystallized colloidal carbon.
According to Nelson, Petroleum Refinery Engineering, Fourth Edition, McGraw-Hill Book Company, New York, N.Y., London, at pages 71-72,
"At gravities below 10 API, water and sediment do not settle out of the oil and such oils cannot be displaced from tanks by water."
The properties reflected above with respect to the black oil residues of Bahrain and the residues deposited from refineries elsewhere are more tractable than the naturally-occurring asphaltic bitumens that one finds in countries such as Venezuela (Orinoco basin) and Trinidad. However, in all instances, these highly viscous residues and asphalt containing materials possess substantial viscosities and are of a generally intractable nature.
The most common method employed for the removal of these viscous materials from their landfill deposits has been by shovel, typically mechanically but sometimes by hand. Some efforts have been made to use archimedean screw-type pumps to more continuously remove them from the landfill deposits. None of these procedures have proven totally adequate for an effectively commercial process for recovering such residues and asphaltic materials from the deposits. The exceptionally high viscosities of these materials makes these procedures slow and irregular, thereby materially increasing the cost of the recovery efforts.
There is need in the industrial recovery of petroleum residue and asphalt deposits for a more efficient and effective method for removing the deposits for subsequent treatment. This invention relates to a process and an apparatus sequence that materially enhances ones ability to effect such recovery.